.Net: Handle rendering a list of strings in a SK prompt (#11780)

### Motivation and Context

Convert lists of strings to a string value correctly

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

Author: markwallace-microsoft

dotnet/src/SemanticKernel.Core/PromptTemplate/KernelPromptTemplate.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Globalization;
 using System.Linq;
 using System.Text;
 using System.Threading;
@@ -99,11 +100,11 @@ private async Task<string> RenderAsync(List<Block> blocks, Kernel kernel, Kernel
             switch (block)
             {
                 case ITextRendering staticBlock:
-                    blockResult = InternalTypeConverter.ConvertToString(staticBlock.Render(arguments), kernel.Culture);
+                    blockResult = ConvertToString(staticBlock.Render(arguments), kernel.Culture);
                     break;
 
                 case ICodeRendering dynamicBlock:
-                    blockResult = InternalTypeConverter.ConvertToString(await dynamicBlock.RenderCodeAsync(kernel, arguments, cancellationToken).ConfigureAwait(false), kernel.Culture);
+                    blockResult = ConvertToString(await dynamicBlock.RenderCodeAsync(kernel, arguments, cancellationToken).ConfigureAwait(false), kernel.Culture);
                     break;
 
                 default:
@@ -187,5 +188,13 @@ private static bool ShouldEncodeTags(bool disableTagEncoding, HashSet<string> sa
         return !disableTagEncoding && block is not TextBlock;
     }
 
+    private static string? ConvertToString(object? value, CultureInfo? culture = null)
+    {
+        if (value is null) { return null; }
+
+        return value is List<string> stringList
+            ? string.Join("\n", stringList)
+            : InternalTypeConverter.ConvertToString(value, culture);
+    }
     #endregion
 }